1. Field of the Invention
The present invention relates to a humidifier and its production method capable of humidifying a dry gas with the moisture that is transmitted from a wet gas through a moisture permeable humidifying membrane, and more particularly, it relates to a humidifier for a fuel cell and its production method that serve to humidify an unreacted gas with the moisture transmitted from an exhaust gas from the fuel cell through a humidifying membrane.
2. Description of the Related Art
A known humidifier is constructed such that a humidifying membrane is clamped by a first separator, which has channel grooves formed to guide a dry gas to flow therealong and is arranged so as to face one side surface of a humidifying membrane, and a second separator which has channel grooves formed to guide a wet gas to flow therealong and is arranged so as to face the other side surface of the humidifying membrane. In order to prevent the blowby of the gases from the outer peripheral portion of the humidifying membrane, the mutually facing peripheral portions of both of the separators are fittingly engaged with each other to compress the humidifying membrane, so that pores in the outer peripheral portion of the humidifying membrane facing the outer peripheral portions of the separators are reduced, thereby shielding the flows of the gases that permeate through the humidifying membrane in its surface directions.
In addition, there is employed a method of bonding between the outer peripheral portions of the separators and the portions of the humidifying membrane facing the outer peripheral portions of the separators by means of a silicone based adhesive material. As general methods of coating such a adhesive material on the outer peripheral portions of the separators suitable for mass production, there are known a method of spray coating, a method of transferring an adhesive material, and so on (see, for example, a first patent document: Japanese patent application laid-open No. 2003-314983).
However, there is a problem that even the reduction of pores in the humidifying membrane by compression thereof can not completely block gas channels in the humidifying membrane, thus permitting leakage of gases therethrough.
In addition, with the method of coating the adhesive material on the outer peripheral portions of the separators, the viscosity of the adhesive is large, and the size of each pore in the humidifying membrane is small, so there arises a problem that in general, the adhesive can not be filled or impregnated into the pores in the humidifying membrane completely or to any satisfactory extent, thus permitting the gases to permeate through inside the humidifying membrane in its surface direction.
In this case, even if a solvent is mixed with the adhesive, so that the viscosity of the adhesive can be lowered to permit the adhesive to be filled up into small pores to a satisfactory extent, there will be another problem that empty pores still remain due to evaporation of the solvent occurring after the filling or impregnation of the pores.
Moreover, if there exist gaps inside the humidifying membrane and in the interfaces between the humidifying membrane and the separators, there will arise a further problem that water or moisture in the humidifying membrane escapes or leaks into the outside due to the capillary action, so moisture in the humidifying membrane is reduced, thus making it impossible to humidify or moisten the dry gas to a sufficient extent.